1. Field of the Invention
The present invention relates to a packaging box, from which stored articles can be easily taken out when a lid plate is opened, and which can endure a compressive stress when a multiple number of the boxes are piled up. The packaging box of the present invention is preferably used for, in particular, storing two or more inner boxes containing recording materials.
2. Description of the Background
Conventionally, packaging boxes represented by corrugated fiberboard boxes have been widely used to store two or more stored articles in a lot. A typical packaging box has a rectangular or rectangular parallelepiped storage space constituted by one bottom plate and four side plates, and has a structure enabling storage of stored articles in a lot. Further, a lid plate is connected to an upper end portion of at least one side plate, and the storage space can be covered from the above or opened by folding the lid plate at the aforementioned upper end portion. A lid plate may be connected to the upper end portions of all the four side plates, or only to the upper end portions of a part of the side plates.
It is generally desired that stored articles should be efficiently stored in such a packaging box. For example, it is often desired that two or more inner boxes should be loaded to fill the storage space of the packaging box substantially without gaps. When inner boxes storing light-shielded medical recording materials are stored, two or more of the inner boxes are loaded without gaps along one side plate of the packaging box. If the inner boxes are loaded without gaps as described above, the space can be efficiently utilized, and risks of moving or damaging of the inner boxes in the packaging box during transport can be reduced.
However, if the inner boxes are loaded without gaps as described above, a problem arises that it becomes difficult to take out the inner boxes from the packaging box. That is, even if it is attempted to take out an inner box by inserting fingers between a side plate of the packaging box and the inner box, it often fails since there is no space for inserting fingers. Therefore, the inner box may be slid out by reversing the packaging box and vertically shaking it while the lid plate of the packaging box is opened. However, the inner box is often slid out too swiftly, and accidents resulting in damage of the inner box content often occur. To avoid such a situation, the side plate of the packaging box may be broken to take out the inner boxes. However, if a part of the packaging box is broken, the packaging box cannot be reused, and therefore it is not preferred.
To solve such a problem, a packaging box has been proposed which is designed so that a space for inserting fingers should be formed in a portion across a side plate and a lid plate when the lid plate of the packaging box is opened. For example, Japanese Patent Laid-open Publication (Kokai) No. 2002-264923 (Publication 1) and Japanese Utility Model Laid-open Publication No 5-19119 (Publication 2) disclose a packaging box in which two parallel cut lines are formed across a side plate and a lid plate connected to the side plate, and two folding lines parallel to each other connecting the end portions of two of the cut lines are formed. When the lid plate of this packaging box is opened, a portion between the two cut lines is bent so that it should protrude outward, thereby providing a space for placing fingers on the inner box.
In the packaging boxes described in Publications 1 and 2, a mechanism for forming a space for placing fingers when the lid plate is opened is provided in facing side plates and lid plates connected to the side plates. And, it is intended that both of the lid plates connected to the facing side plates are opened to form two spaces, and fingers are inserted into each space to hold the both ends of the inner box and thereby take out the inner box. However, because parallel cut lines are formed along the same direction in the facing side plates and the lid plates connected to the side plates in these packaging boxes, they suffer from a problem of poor strength against a compressive stress imposed along the direction of the cut lines. Such a stress is likely to be imposed when a multiple number of the packaging boxes are piled up, and problems are likely to occur in practical use.
Further, because at least four cut lines and at least four folding lines must be formed in the packaging boxes described in Publications 1 and 2, time and labor are required for manufacture of the boxes. Furthermore, a lid plate must be connected to each of the facing side plates in order to form the mechanism for forming a space in the packaging boxes described in Publications 1 and 2, the degree of freedom in the design of the packaging box is limited. Moreover, to take out an inner box by holding both ends of the box with fingers as described in Publications 1 and 2, both of the lid plates connected to the facing side plates must be opened, and it cannot be considered that the time required to take out the inner box is short.